Archive Article: 1997/07/05

5 July 1997

Savings, whether its the agrochemical or the kit, underpinned this years Sprays and Sprayers. Tia Rund reports.

MOST would agree that, in theory at least, patch spraying offers potential to save on spray chemicals.

Graminicide usage could be halved. And total herbicide and fungicide could be cut by a quarter, claims Silsoe Research Institute, which announced its latest step towards turning theory into reality at the Cambs event.

Having judged technical feasibility using an experimental rig and MAFF/HGCA funding, SRI now plans to assess practical impact with a commercial prototype sprayer developed in collaboration with Micron Sprayers.

Microns technical director John Clayton explains his companys involvement: "Our guiding philosophy has always been one of developing better and more efficient application methods, such as the CDA concept which changed the fundamental rules of spraying.

"Theres potential with patch spraying to also change the rules. Theres no longer a need to be governed by chemical label recommendations which assume blanket application rates. Micron is taking the stance of a catalyst and invites participation and support from others."

The first aim is to test market response to the 24m prototype prior to commercialising products hopefully within 12-18 months time. The system has been designed to be directly compatible with existing sprayer systems and to be retro-fitted.

It incorporates two spray nozzles, each fitted with a pneumatic on/off valve, at each position along the boom. A GPS-controlled compressed air system adjusts application rate in the range 30-150% of recommended dose by switching between one or other, or both.

This overcomes the limitations of a single conventional nozzle, where the only way to change output is to change pressure. This also has the undesirable effect of changing spray distribution pattern and droplet size outside of a narrow range – about 20% around a nominal value.

But, in the development of the prototype, an important feature of the earlier test rig has been bypassed. Injection metering gave the ability to control the proportion of ingredients in a spray mix as well as the dose rate of a single product.

Considering that most herbicides are applied in tank mix, injection metering will continue as part of SRIs work. It does, however, require cooperation from the agrochemical companies.

One manufacturer which seemed to be at least matching SRIs patch spraying progress was Chavtrac. Its variable rate, GPS controlled Spra Coupe will be available by spring next year.

It can also handle multiple products. The production prototype on show at Sprays and Sprayers can accommodate a three-way tank mix – with one chemical in the tank and up to two more metered through Raven direct injection pumps into the spray line. Changing pump speed from static to full speed varies the application rate accordingly.

Raven also provides both the console to control as many as five chemicals, liquid and solid, and the GPS receiver/controller. And Chavtrac has developed Patchwork – the software system which provides the interface with yield mapping systems.

Beyond the potential for patch spraying, having separate tanks for different chemicals gives the flexibility to spray consecutive crops without having to change the mix in between.

Other sprayer manufacturers are poised on the brink of GPS controlled variable application. Knight Farm Machinery, for instance, claims that the combination of AirJet twin fluid nozzles and TeeJet Airmatic controller gives sufficient rate variation without losing the desired droplet spectrum.

In terms of application technology, everything is in place. The missing link in each case seems to be the spatial map that determines the areas to receive insurance doses and those which need full rate.

"But for easily defined problems using the operators ability to detect and positional information from GPS, mapping systems are very near," said Dr Paul Miller of SRI.

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